Uplink power control using beamforming to compensate for path loss

ABSTRACT

The technique of beamforming is to be adopted in 5G NR systems in both DL and UL directions to combat the effect of acute path loss in the Giga hertz frequency region. With beamforming, the measured path loss in the UL and DL directions will be different even if the same carrier frequency is used for both DL and UL, due to the fact that the antenna gains are not unity as in the case in LTE/LTE-A systems. In view of this, embodiments of the present invention provide method and apparatus to handle the mechanism of UL transmit power control.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 15/871,089, filed on Jan. 15, 2018, which claims the benefit of U.S.Provisional Application No. 62/475,816, filed on Mar. 23, 2017. Theentire contents of the related applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to transmit power control, and moreparticularly, to methods and apparatus for performing transmit powercontrol in next-generation cellular communications systems, such as 5GNew Radio system.

2. Description of the Prior Art

Path loss (PL) is the phenomenon that the electromagnetic signalsattenuate when propagating from the transmitter to the receiver. Theformula for path loss is widely known and can be given as:

${PL} = {\frac{P_{r}}{P_{t}} = {G_{t}{G_{r}\left( \frac{\lambda}{4\pi\; d} \right)}^{2}}}$where P_(t) and P_(r) represent the transmit and the receive powerrespective, G_(t) and G_(r) represent the transmit and receive antennagains in linear value respectively, λ is the wavelength, and d is thedistance between the transmitter and the receiver. It can be observedthat, as long as the transmitter and the receiver both use unity-gain,omnidirectional antennas, the path loss between the transmitter and thereceiver depends only on the wavelength. In other words, the magnitudeof “PL” can be considered the same for both the DL and UL directions ifthe operating frequencies of DL and UL are not too far apart. This isthe case in most existing cellular communication systems, includingLTE/LTE-A, where a user equipment (UE) estimates the PL by measuring howmuch a known cell-specific reference signal attenuates when it isreceived. The UE then accounts for the factor of PL by increasing itstransmit power by the same magnitude when performing UL transmissions.

In cellular communication systems, uplink (UL) power control is atechnique for the UEs to adjust the transmit power toward the basestation in order to maintain a desired power level. The purpose of ULpower control is many-fold, including the already-mentioned compensationfor path loss, causing less interference to other UEs, guaranteeing acertain transmission error performance, and lowering the powerconsumption. In LTE/LTE-A systems, the mechanism of UL power controlconsists of both an open-loop (OL) component and a closed-loop (CL)component. Details of the UL power control mechanism can be found in areleased document: ““Physical Layer Procedures,” 3GPP TS 36.213,V14.1.0, 2017-01”.

In 5G new radio (NR) systems, it has been agreed that the UL powercontrol mechanism also supports both an open-loop part based on pathloss estimate, and a closed-loop part based on network signaling. Ingeneral, the 5G NR system reuses many of the design principles inLTE/LTE-A systems; yet at the same time introduces a few new features.Some of the features, including supporting different numerologies,different UL waveforms, and beamforming-based system access, couldpotentially impact the UL power control mechanism as specified for theLTE/LTE-A systems.

Different numerologies will be supported in 5G NR systems, includingdifferent subcarrier frequency spacing, and different OFDM symbolduration. A scheduling unit is defined as the smallest time frequencyresource used for scheduling one DL or one UL transmission for a UE. Thenumber of resource elements in a scheduling unit is expected to be thesame across different numerologies. Both discrete Fourier transform(DFT)-spread OFDM and cyclic prefix (CP)-OFDM for UL transmissions areboth supported in 5G NR systems.

Carrier frequencies range from several MHz to as high as 60 GHz will besupported in 5G NR systems. As can be observed in the path loss formula,the path loss worsens along with decreasing wavelength, or equivalently,with increasing carrier frequency. It thus follows that for 5G NRsystems deployed in the frequency range close to 60 GHz, the effect ofpath loss is a big challenge to the system design. Antenna arrays thatachieves a high transmit antenna gain as well as a high receive antennagain, or the beamforming gain, have been proposed to be supported in the5G NR systems as a building block right from the beginning. This impliesthat the fundamental system information as well as cell-specificreference signals are all transmitted using beamformed signals withantenna gains larger than 1, for both DL and UL directions.

SUMMARY OF THE INVENTION

It is one objective of the present invention to provide methods andapparatus for determine and performing uplink power control innext-generation cellular communications systems, such as 5G New Radiosystem. Since the next-generation cellular adopts the beamformingtechnology, embodiments of the present invention relies on calculationson antenna gains of antenna configuration to determine the uplinktransmit power.

According to one embodiment, a method for a user equipment (UE) toperform uplink transmit power control is provided. The UE comprises:receiving, from a base station, a control information comprising atleast an antenna configuration; determining uplink transmit power of atleast one uplink signal based on at least the control information; andtransmitting the at least one uplink signal with the determined uplinktransmit power to the base station.

According to one embodiment, a user equipment (UE) is provided. The UEcomprises: a communication interfacing unit; a storage unit and aprocessing circuit. The communication interfacing unit is arranged toreceive, from a base station, control information comprising at least anantenna configuration. The storage unit is arranged to store programcode. The processing circuit is arranged to execute the program codethereby to perform steps of determining uplink transmit power of atleast one uplink signal based on at least the control information,wherein the communication interfacing unit is arranged to transmit theat least one uplink signal with the determined uplink transmit power tothe base station.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a wireless communication system 10according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a communication device 20 according toone embodiment of the present invention.

FIG. 3 illustrates gains of antenna configurations of UE and basestation in uplink and downlink transmission.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a wireless communication system 10according to an example of the present invention. The wirelesscommunication system 10 is briefly composed of a network and a pluralityof communication devices. The network and a communication device maycommunicate with each other via one or more carriers of licensed band(s)and/or unlicensed band(s). In FIG. 1, the network and the communicationdevices are simply utilized for illustrating the structure of thewireless communication system 10. Practically, the network may be anevolved UTRAN (E-UTRAN) including at least one evolved NB (eNB), and/ora next-generation NB (gNB), and/or at least one relay in a long termevolution (LTE) system, a LTE-Advanced (LTE-A) system or an evolution ofthe LTE-A system, e.g., a 5G NR system. The eNB or the relay may betermed as a base station.

FIG. 2 is a schematic diagram of a communication device 20 according toan example of the present invention. The communication device 20 can bea user equipment (UE) or the network shown in FIG. 1, but is not limitedherein. The communication device 20 may include a processing means 200such as a microprocessor or an Application Specific Integrated Circuit(ASIC), a storage unit 210 and a communication interfacing unit 220. Thestorage unit 210 may be any data storage device that can store a programcode 214, accessed by the processing means 200. Examples of the storageunit 210 include but are not limited to a subscriber identity module(SIM), read-only memory (ROM), flash memory, random-access memory (RAM),hard disk, and optical data storage device. The communicationinterfacing unit 220 is preferably a radio transceiver, and can transmitand receive wireless signals according to processing results of theprocessing means 200. The program code 214 implementing any of solutionsabove may be stored in the storage unit 210 and executed in theprocessing means 200.

To determine the transmit power, a base station transmits a DL referencesignal to a UE using a first transmit antenna configuration for apurpose of path loss measurement. The gain of the first transmit antennaconfiguration gain is hereinafter denoted by G_(t) ^(DL). The UEreceives the DL reference signal using a first receive antennaconfiguration. The gain of the first receive antenna configuration gainis hereinafter denoted by G_(r) ^(DL). The UE transmits an UL signal tothe base station using a second transmit antenna configuration and an ULpower control formula. The gain of the second transmit antennaconfiguration gain is hereinafter denoted by G_(t) ^(UL). The UE usesthe UL power control formula to determine an UL transmit power for theUL signal. Procedures for determining the UL power control formula areelaborated in the following. The base station receives the UL signalusing a second receive antenna configuration. The gain of the secondreceive antenna configuration gain is denoted by G_(r) ^(UL). Anillustrative diagram is illustrated in FIG. 3. Specifically, the antennaconfiguration may comprise at least a beamforming configuration, and/ora beamformed signal configuration. In one embodiment, the beamformedsignal configuration may comprise a configuration of a beamformed ULreference signal or an index of a beamformed UL reference signal.Furthermore, the index of the beamformed UL reference signal may be asounding reference signal resource index (SRI) in one embodiment.

The antenna gains in following descriptions are all represented in dBscale. For example, let Ĝ_(t) ^(DL) denote the gain of the firsttransmit antenna configuration in linear value. We have G_(t) ^(DL)=10log₁₀(Ĝ_(t) ^(DL)). Note that it is not precluded for the first transmitantenna configuration to be the same as the second receive antennaconfiguration. In other words, the base station uses the same antennaconfiguration for transmitting the DL reference signal to the UE andreceiving the UL signal from the UE. And in this case we have G_(t)^(DL)=G_(r) ^(UL). Similarly, it is not precluded for the secondtransmit antenna configuration to be the same as the first receiveantenna configuration. In this case, the UE uses the same antennaconfiguration for receiving the DL reference signal from the basestation and transmitting the UL signal to the base station. And we haveG_(r) ^(UL)=G_(r) ^(DL).

The UL transmit power is determined based on a closed-loop (CL) powercontrol parameter, an open-loop power control (CL) parameter and a pathloss parameter. These parameters are associated with transmit antennagain and receive antenna gain of the antenna configuration of the UE andthe base station. During the communication, the base station may notifythe UE of the antenna configuration used for the communication bysending control information to the UE. Accordingly, the UE determinesthe CL power control parameter, the OL power control parameter and thepath loss parameter according to the antenna configuration, and therebyto determine the UL transmit power. Alternatively, the base station maydirectly determine the OL the CL power control parameter, the OL powercontrol parameter and the path loss parameter according to the antennaconfiguration, and send the control information including the determinedparameters to the UE. As such, the UE determines the UL transmit poweraccording to the parameters determined and sent by the base station.

As mentioned above, the base station and the UE may comprise the storageunit 210 storing the program code 214 as illustrated in FIG. 2. The basestation and the UE may also comprise the processing circuit 200. Whenthe program code 214 executed by the processing circuit 200, the UE orthe base station determines the above-identified parameters.Accordingly, the UE determine the UL transmit power and have an ULtransmit power control on the communication interfacing unit 220.

Closed-Loop Control Using Dynamic Signaling

In one embodiment, the base station or the UE calculates a gaindifference between the gain of the first transmit antenna configurationand the gain of the second receive antenna configuration, i.e., (G_(t)^(DL)−G_(r) ^(UL)). This calculation can be directly achieved by thebase station since the base station typically determines the antennaconfiguration for the UE. Alternatively, this can be achieved by the UEsince the UE may be notified of the antenna configuration from thecontrol information sent by the base station.

The base station or the UE determines a first closed-loop (CL) powercontrol parameter for taking into account at least the above-mentionedgain difference. In one embodiment, the base station or the UE performsthis calculation by first assuming a unity antenna gain for both thefirst transmit antenna configuration and the second receive antennaconfiguration. Then, the base station or the UE calculates a second CLpower control parameter in a way analogous to that introduced in““Physical Layer Procedures,” 3GPP TS 36.213, V14.1.0, 2017-01” forLTE/LTE-A systems, where unity antenna gain is employed. Finally, thebase station or the UE obtains the first CL power control parameter bycombining the gain difference of antenna gain (G_(t) ^(DL)−G_(r) ^(UL)),and the second CL power control parameter.

If the CL power control parameter is determined by the base station, thebase station will transmit the CL power control parameter to the UEusing dynamic signaling in a DL control signal. The UE receives the DLcontrol signal. The UE adjusts the UL transmit power for transmittingthe UL signal following the first CL power control parameter in the DLcontrol signal. In one embodiment, the UE determines the UL powerfollowing the UL power control formula as:

$\min\left\{ \begin{matrix}{P_{{CMAX},c}(i)} \\{{10{\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O\;\_\;{PUSCH}},c}(j)} + {{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} +} \\\left( {{f_{c}(i)} + \left( {G_{t}^{DL} - G_{r}^{UL}} \right)} \right)\end{matrix} \right.$where P_(CMAX,c)(i) is a transmit power limit for the UL signal takinginto account other potential concurrent UL transmissions with higherpriority (e.g., UL control signals), f_(c)(i)+(G_(t) ^(DL)−G_(r) ^(UL))is the first CL power control parameter in the DL control signaltransmitted by the base station (or determined by UE itself), thefunctionalities of the rest parameters are similarly defined as in the““Physical Layer Procedures,” 3GPP TS 36.213, V14.1.0, 2017-01”.

The first CL power control parameter can be accumulative, which meansthe UE adjusts the UL power by simply adding the current UL transmitpower and the first CL power control parameter transmitted from the basestation (or determined by UE itself) in the dynamic DL control signal.Alternatively, the first CL power control parameter can be absolute,which means the UE negates the previous received CL power controlparameter and apply the current received CL power control parameter.

In one embodiment, the UE may comprise different registers to recordaccumulated values of the first CL power control parameters with respectto different antenna configurations. Each register may hold anaccumulated value of the first CL power control parameter with respectto a specific antenna configuration. When the antenna configurationchanges, the UE may read accumulated value from a different register todetermine the uplink transmit power.

Open-Loop Control Using Higher Layer Signaling

In one embodiment, the base station or the UE calculates againdifference between the gain of the first transmit antenna configurationand the gain of the second receive antenna configuration, i.e. (G_(t)^(DL)−G_(r) ^(UL)). Similarly to the determination of the CL powercontrol parameter, this calculation can be directly achieved by the basestation since the base station typically determines the antennaconfiguration for the UE. Alternatively, this can be achieved by the UEsince the UE may be notified of the antenna configuration from thecontrol information sent by the base station.

The base station or the UE determines a first UE-specific open-loop (OL)power control parameter for the UE taking into account at least theabove-mentioned gain difference. In one embodiment, the base station orthe UE performs this calculation by first assuming a unity antenna gainfor both the first transmit antenna configuration and the second receiveantenna configuration. Then, the base station or the UE calculates asecond UE-specific OL power control parameter in a way analogous to thatintroduced in ““Physical Layer Procedures,” 3GPP TS 36.213, V14.1.0,2017-01” for LTE/LTE-A systems, where unity antenna gain is employed.Finally, the base station or the UE obtains the first UE-specific OLpower control parameter by combining the difference of antenna gain(G_(t) ^(DL)−G_(r) ^(UL)), and the second UE-specific OL power controlparameter.

If the OL power control parameter is determined by the base station, thebase station transmits the UE-specific OL power control parameter to theUE using a higher layer signaling. The UE receives the higher layersignaling. The UE adjusts the UL transmit power for transmitting the ULsignal by applying the first UE-specific OL power control parameter. Inone embodiment, the UE determines the UL power following the UL powercontrol formula as:

$\min\left\{ {{\begin{matrix}{P_{{CMAX},c}(i)} \\{{10{\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O\;\_\;{PUSCH}},c}(j)} + {{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} +} \\\left( {{f_{c}(i)} + \left( {G_{t}^{DL} - G_{r}^{UL}} \right)} \right)\end{matrix}{P_{{O\;\_\;{PUSCH}},c}(j)}} = {\left( {{P_{{O\;\_\;{UE}\;\_\;{PUSCH}},c}(j)} + G_{t}^{DL} - G_{r}^{UL}} \right) + {P_{{O\;\_\;{NOMINAL}\;\_\;{PUSCH}},c}(j)}}} \right.$where (P_(O_UE_PUSCH,c)(j)+G_(t) ^(DL)−G_(r) ^(UL)) is the firstUE-specific OL power control parameter in the higher layer signalingtransmitted by the base station (or determined by UE itself), thefunctionalities of the rest parameters are similarly defined as in““Physical Layer Procedures,” 3GPP TS 36.213, V14.1.0, 2017-01”.Both BS and UE Account for Antenna Gain Difference I

In one embodiment, the UE calculates a first gain difference between thegain of the second transmit antenna configuration and the gain of thefirst receive antenna configuration, i.e., G_(r) ^(DL)−G_(t) ^(UL). Thebase station calculates a second gain difference between the gain of thefirst transmit antenna configuration and the gain of the second receiveantenna configuration, i.e., G_(t) ^(DL)−G_(r) ^(UL). The base stationthen calculates a CL power control parameter using at least the secondgain difference. The base station transmits the CL power controlparameter to the UE using dynamic signaling in a DL control signal. TheUE receives the DL control signal. The UE determines the UL powercontrol formula using at least the first gain difference, and the CLpower control parameter in the DL control signal. In one embodiment, theUE determines the UL power control formula as:

$\min\left\{ \begin{matrix}{P_{{CMAX},c}(i)} \\{{10{\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O\;\_\;{PUSCH}},c}(j)} + {{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} +} \\\left( {\left( {{f_{c}(i)} + \left( {G_{t}^{DL} - G_{r}^{UL}} \right)} \right) + G_{r}^{DL} - G_{t}^{UL}} \right)\end{matrix} \right.$where ((f_(c)(i)+(G_(t) ^(DL)−G_(r) ^(UL))) is the CL power controlparameter in the DL control signal transmitted by the base station, andG_(r) ^(DL)−G_(t) ^(UL) is the first gain difference calculated by theUE. The UE then determines the UL transmit power for the UL signalfollowing the UL power control formula.Both BS and UE Account for Antenna Gain Difference Case II

In one embodiment, the UE calculates a first gain difference between thegain of the second transmit antenna configuration and the gain of thefirst receive antenna configuration, i.e. G_(r) ^(DL)−G_(t) ^(UL). Thebase station calculates a second gain difference between the gain of thefirst transmit antenna configuration and the gain of the second receiveantenna configuration, i.e. G_(t) ^(DL)−G_(r) ^(UL). The base stationthen calculates a UE-specific OL power control parameter using at leastthe second gain difference. The base station transmits the UE-specificOL power control parameter to the UE using a higher layer signaling. TheUE receives the higher layer signaling. The UE determines the UL powercontrol formula using at least the first gain difference, and theUE-specific OL power control parameter in the higher layer signaling. Inone embodiment, the UE determines the UL power control formula as:

$\min\left\{ {{\begin{matrix}{P_{{CMAX},c}(i)} \\{{10{\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O\;\_\;{PUSCH}},c}(j)} + {{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} +} \\\left( {{f_{c}(i)} + \left( {G_{r}^{DL} - G_{t}^{UL}} \right)} \right)\end{matrix}{P_{{O\;\_\;{PUSCH}},c}(j)}} = {\left( {{P_{{O\;\_\;{UE}\;\_\;{PUSCH}},c}(j)} + G_{t}^{DL} - G_{r}^{UL}} \right) + {P_{{O\;\_\;{NOMINAL}\;\_\;{PUSCH}},c}(j)}}} \right.$where (P_(O_UE_PUSCH,c)(j)+G_(t) ^(DL)−G_(r) ^(UL)) is the UE-specificOL power control parameter in the higher layer signaling transmitted bythe base station, and G_(r) ^(UL)−G_(t) ^(UL) is the first differencecalculated by the UE. The UE then determines the UL transmit power forthe UL signal following the UL power control formula.

According to various embodiment of the present invention, theabove-mentioned “UL signal” could be regular user data, UL referencesignal, or UL control signal. In additionally, The UE can also transmita power headroom report to the base station to report the remainingavailable power for performing UL transmission using the UL powercontrol formula proposed in the above descriptions.

In summary, disclosed embodiments of the present invention providesmanners to determine the uplink power control for the UE in a nextgeneration cellular communications systems, such as 5G New Radio system.As the next generation cellular communications systems uses adopts thebeamforming technology, the disclosed embodiments of the presentinvention introduces calculations on transmit and receive antenna gainsof the antenna configuration into the determination of the uplinktransmit power control.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for a user equipment (UE) to performuplink transmit power control, comprising: receiving, from a basestation, a control information comprising at least a UE antennaconfiguration, wherein the UE antenna configuration comprises at least asounding reference signal resource index (SRI); receiving a downlinkreference signal from the base station; determining an open-loop (OL)power control parameter according to the UE antenna configuration;determining a path loss parameter according to the UE antennaconfiguration and the downlink reference signal; determining uplinktransmit power of at least one uplink signal based on at least one ofthe control information, the OL power control parameter, and the pathloss parameter; and transmitting the at least one uplink signal with thedetermined uplink transmit power to the base station.
 2. A userequipment (UE), comprising: a communication interfacing unit, arrangedto receive, from a base station, a control information comprising atleast a UE antenna configuration, wherein the UE antenna configurationcomprises at least a sounding reference signal resource index (SRI),wherein the communication interfacing unit is further arranged toreceive a downlink reference signal from the base station; a storageunit, arranged to store program code; and a processing circuit, arrangedto execute the program code thereby to perform steps of: determining anopen-loop (OL) power control parameter according to the UE antennaconfiguration; determining a path loss parameter according to the UEantenna configuration and the downlink reference signal; and determininguplink transmit power of at least one uplink signal based on at leastone of the control information, the OL power control parameter, and thepath loss parameter, wherein the communication interfacing unit isfurther arranged to transmit the at least one uplink signal with thedetermined uplink transmit power to the base station.
 3. The UE of claim2, wherein the processing circuit is arranged to execute the programcode thereby further to perform at least one step of: determining aclosed-loop (CL) power control parameter according to the UE antennaconfiguration.
 4. The UE of claim 3, wherein the processing circuit isarranged to execute the program code thereby further to perform stepsof: calculating a gain difference between a transmit antenna gain and areceive antenna gain of the base station according to the UE antennaconfiguration; determining a second CL power control parameter byassuming the transmit antenna gain and the receive antenna gain of thebase station as unity; and combining the gain difference between thetransmit antenna gain and the receive antenna gain of the base stationand the second CL power control parameter thereby to obtain a first CLpower control parameter.
 5. The UE of claim 4, wherein the processingcircuit is arranged to execute the program code thereby to furtherperform steps of: determining a gain difference between a receiveantenna gain and a transmit antenna gain of the UE according to the UEantenna configuration; and determining the transmit power according tothe determined CL power parameter and the gain difference between thereceive antenna gain and the transmit antenna gain of the UE.
 6. The UEof claim 2, wherein the processing circuit is arranged to execute theprogram code thereby to further perform steps of: calculating a gaindifference between a transmit antenna gain and a receive antenna gain ofthe base station according to the UE antenna configuration; determininga second UE-specific OL power control parameter by assuming the transmitantenna gain and the receive antenna gain of the base station as unity;and combining the gain difference between the transmit antenna gain andthe receive antenna gain of the base station and the second UE-specificOL power control parameter thereby to obtain a first UE-specific OLpower control parameter.
 7. The UE of claim 6, wherein the processingcircuit is arranged to execute the program code thereby to furtherperform steps of: determining a gain difference between a receiveantenna gain and a transmit antenna gain of the UE according to the UEantenna configuration; and determining the uplink transmit poweraccording to the determined OL power control parameter and the gaindifference between the receive antenna gain and the transmit antennagain of the UE.